The hard outer shell of a popcorn kernel, known as the pericarp, is a tough layer that is central to the entire popping process. Without this specific type of outer casing, the familiar fluffy snack would not exist.
The Science of the Pop
The pericarp is a strong outer shell with a crystalline structure, making it highly resistant to moisture escaping. It effectively turns each popcorn kernel into a miniature pressure vessel. Inside the kernel, a small amount of water is stored within a starchy center. As the kernel is heated to around 180°C (356°F), this water turns into steam.
This steam generates immense pressure, building to levels as high as nine times that of the atmosphere at sea level. Once the pressure becomes too great for the pericarp to contain, it ruptures. This sudden release of pressure causes the superheated, gelatinous starch inside to rapidly expand and cool, forming the white, puffy structure of popped popcorn.
Anatomy of a Popcorn Kernel
A popcorn kernel has three main components. The outermost layer is the pericarp, the hard, protective hull. This shell encases the endosperm, which is the most substantial part of the kernel. The endosperm is composed of starch and contains the water needed for popping.
Nestled within the endosperm is the germ, the kernel’s embryo. While the germ is the living part that would grow into a plant, it is not directly involved in the popping process. The endosperm provides the starch and moisture, while the pericarp provides the containment and pressure seal.
The Hull Truth
After the kernel explodes, the shattered fragments of the pericarp are what we refer to as the hull. These are the hard, flaky pieces that often get lodged in teeth and gums. This has led to the marketing of “hulless” popcorn, though the name is misleading. No popcorn can be truly hulless, because a pericarp is required for the kernel to pop.
“Hulless” or “thin-hulled” popcorn varieties are cultivated to have a much thinner and more tender pericarp. When these kernels pop, the hull shatters into smaller, finer pieces that are less noticeable. The result is a more tender piece of popcorn that feels as if it has no hull.